feat(sp14): 5-lane Inbox UI with Payer-Rejected acknowledge action

Closes the gap between the SP10 backend (5 lanes) and the SP6
frontend (4 lanes). The Payer-Rejected lane (277CA STC A4/A6/A7)
is now rendered alongside Rejected/Candidates/Unmatched/Done,
with an Acknowledge bulk action that drops claims from the
working surface without erasing the original 277CA rejection
event (audit log stays intact, SP11).

Backend:
* Migration 0010: add payer_rejected_acknowledged_at +
  payer_rejected_acknowledged_actor columns + partial index.
* db.py: surface the two new columns on the Claim model.
* inbox_lanes.py: filter acknowledged claims out of the
  payer_rejected lane; expose the new fields on the row payload
  for forward-compat (e.g. a future 'Recently acknowledged' view).
* api.py:
  - POST /api/inbox/payer-rejected/acknowledge
    Bulk-acknowledge. Idempotent. Returns transitioned /
    already_acked / not_found / not_rejected counts so the UI
    can show '3 of 5 were already acknowledged' on a noop bulk.
    Writes a 'claim.payer_rejected_acknowledged' event to the
    SP11 hash-chained audit log.
  - GET /api/inbox/export.csv: accept 'payer_rejected' lane.
* test_acks.py: bump user_version assertion to 10.
* test_lane_filter_acknowledged.py: 4 tests for the lane filter
  and forward-compat row payload.
* test_payer_rejected_acknowledge.py: 6 tests for the endpoint
  (happy path, idempotency, no-op on non-rejected, missing
  ids, 400 on empty, audit-log wiring + chain integrity).

Frontend:
* lib/inbox-api.ts: add payer_rejected to InboxLanes, add
  acknowledgePayerRejected(), update exportInboxCsvUrl union.
* hooks/useInboxLanes.ts: add payer_rejected to initial state.
* hooks/useInboxLanes.test.ts: add payer_rejected to mocks.
* components/inbox/BulkBar.tsx: add 'payer_rejected' lane with
  Acknowledge action (no Resubmit, no Dismiss — payer-rejected
  is not eligible for either).
* components/inbox/BulkBar.test.tsx: add payer_rejected test.
* pages/Inbox.tsx: render the 5th lane, hook up onAcknowledge,
  include payer_rejected in the needEyes count.
* pages/Inbox.test.tsx: 3 new tests (5-lane render, need-eyes
  count, acknowledge action hits the right endpoint).
* components/inbox/InboxHeader.tsx: doc comment now explains
  why payer_rejected rolls up into need-eyes.

Pre-existing typecheck warnings in BulkBar.test.tsx / InboxRow
.test.tsx / Lane.tsx / download.test.ts are unchanged from
main — not touched here.

Test counts: backend 724 -> 734 (+10). Frontend 350 -> 354 (+4).

backend/src/cyclone/api.py

@@ -1105,6 +1105,78 @@ def inbox_dismiss_candidates(body: dict):
     return {"ok": True, "dismissed_count": len(pairs)}
 
 
+# ---------------------------------------------------------------------------
+# SP14: Payer-Rejected acknowledge
+#
+# Operator hits "Acknowledge" on the Payer-Rejected Inbox lane to clear
+# the claim from the working surface. We don't delete the rejection
+# (the original payer_rejected_* fields stay for SP11 audit), we just
+# set payer_rejected_acknowledged_at so the lane query filters it out.
+#
+# Idempotent: re-acknowledging an already-acknowledged claim is a noop
+# (the timestamp is not bumped). Returns the count actually transitioned
+# so the UI can show "3 of 5 were already acknowledged".
+# ---------------------------------------------------------------------------
+@app.post("/api/inbox/payer-rejected/acknowledge")
+def inbox_acknowledge_payer_rejected(body: dict):
+    """Mark Payer-Rejected claims as acknowledged by the operator."""
+    claim_ids = body.get("claim_ids") or []
+    actor = body.get("actor") or "operator"
+    if not isinstance(claim_ids, list) or not claim_ids:
+        raise HTTPException(400, "claim_ids must be a non-empty list")
+    if not all(isinstance(c, str) for c in claim_ids):
+        raise HTTPException(400, "claim_ids must be a list of strings")
+
+    with db.SessionLocal()() as session:
+        from cyclone.db import Claim
+        now = datetime.now(timezone.utc)
+        transitioned = 0
+        already_acked = 0
+        not_found = 0
+        not_rejected = 0
+        for cid in claim_ids:
+            claim = session.get(Claim, cid)
+            if claim is None:
+                not_found += 1
+                continue
+            if claim.payer_rejected_at is None:
+                not_rejected += 1
+                continue
+            if claim.payer_rejected_acknowledged_at is not None:
+                already_acked += 1
+                continue
+            claim.payer_rejected_acknowledged_at = now
+            claim.payer_rejected_acknowledged_actor = actor
+            transitioned += 1
+            # SP11: audit event for the acknowledge action.
+            try:
+                from cyclone.audit_log import append_event, AuditEvent
+                append_event(session, AuditEvent(
+                    event_type="claim.payer_rejected_acknowledged",
+                    entity_type="claim",
+                    entity_id=claim.id,
+                    actor=actor,
+                    payload={
+                        "payer_rejected_status_code": claim.payer_rejected_status_code,
+                        "payer_rejected_by_277ca_id": claim.payer_rejected_by_277ca_id,
+                    },
+                ))
+            except Exception:  # noqa: BLE001
+                # Audit append is best-effort; don't block the operator's
+                # acknowledge action on an audit-log failure.
+                pass
+        if transitioned:
+            session.commit()
+
+    return {
+        "ok": True,
+        "transitioned": transitioned,
+        "already_acked": already_acked,
+        "not_found": not_found,
+        "not_rejected": not_rejected,
+    }
+
+
 @app.post("/api/inbox/rejected/resubmit")
 def inbox_resubmit_rejected(
     request: Request,
@@ -1202,7 +1274,7 @@ def inbox_resubmit_rejected(
 @app.get("/api/inbox/export.csv")
 def inbox_export_csv(lane: str):
     """Stream a CSV for a single lane."""
-    if lane not in {"rejected", "candidates", "unmatched", "done_today"}:
+    if lane not in {"rejected", "candidates", "unmatched", "done_today", "payer_rejected"}:
         raise HTTPException(400, f"unknown lane: {lane}")
     dismissed_pairs = getattr(app.state, "dismissed_pairs", set())
     with db.SessionLocal()() as session:

backend/src/cyclone/db.py

@@ -239,6 +239,16 @@ class Claim(Base):
     payer_rejected_by_277ca_id: Mapped[Optional[str]] = mapped_column(
         String(64), nullable=True
     )
+    # SP14: when the operator hits "Acknowledge" on the Payer-Rejected
+    # lane, we set this timestamp. The lane query filters on it being
+    # NULL so acknowledged claims drop out of the working surface. The
+    # original payer_rejected_* fields stay intact for audit (SP11).
+    payer_rejected_acknowledged_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    payer_rejected_acknowledged_actor: Mapped[Optional[str]] = mapped_column(
+        String(64), nullable=True
+    )
     resubmit_count: Mapped[int] = mapped_column(
         Integer, nullable=False, default=0, server_default=text("0")
     )

backend/src/cyclone/inbox_lanes.py

@@ -73,6 +73,12 @@ def _claim_to_row(
         "payer_rejected_reason": c.payer_rejected_reason,
         "payer_rejected_status_code": c.payer_rejected_status_code,
         "payer_rejected_by_277ca_id": c.payer_rejected_by_277ca_id,
+        # SP14: acknowledgment tracking. Always null on the lane
+        # (we filter acknowledged claims out) but exposed for
+        # forward-compat if we later add a "Recently acknowledged"
+        # inspector view.
+        "payer_rejected_acknowledged_at": _isoformat(c.payer_rejected_acknowledged_at),
+        "payer_rejected_acknowledged_actor": c.payer_rejected_acknowledged_actor,
     }
 
 
@@ -192,8 +198,15 @@ def compute_lanes(session: Session, *, dismissed_pairs: Iterable[frozenset]) ->
     # by the payer after we submitted a syntactically-valid file).
     # We don't filter by Claim.state here because the claim may still
     # be in SUBMITTED state — the payer just hasn't paid it yet.
+    #
+    # SP14: filter out claims the operator has already acknowledged.
+    # The original payer_rejected_* fields stay intact for audit;
+    # only the working surface (this lane) is filtered.
     payer_rejected_claims = (
-        session.query(Claim).filter(Claim.payer_rejected_at.is_not(None)).all()
+        session.query(Claim)
+        .filter(Claim.payer_rejected_at.is_not(None))
+        .filter(Claim.payer_rejected_acknowledged_at.is_(None))
+        .all()
     )
     pr_matched, pr_total = _line_count_lookup(session, payer_rejected_claims)
     matched_counts.update(pr_matched)

backend/src/cyclone/migrations/0010_payer_rejected_acknowledged.sql

@@ -0,0 +1,22 @@
+-- version: 10
+-- SP14: Payer-Rejected lane acknowledge
+-- When the operator reviews a payer-rejected claim, they hit the
+-- "Acknowledge" bulk action. We mark the claim with the timestamp so
+-- the lane query can filter it out (it stays in the DB for audit but
+-- doesn't show up in the operator's working surface).
+--
+-- Why a separate column instead of clearing payer_rejected_at:
+--   * Audit trail: SP11's hash-chained audit_log needs the *original*
+--     rejection event intact. Clearing the timestamp would erase the
+--     evidence of the payer saying "no" — exactly what auditors want
+--     to see.
+--   * Reconciliation: future SPs that match payer-rejected claims
+--     against appeals (e.g. SP17) can still see the original status
+--     code and reason.
+
+ALTER TABLE claims ADD COLUMN payer_rejected_acknowledged_at TEXT;
+ALTER TABLE claims ADD COLUMN payer_rejected_acknowledged_actor TEXT;
+
+CREATE INDEX idx_claims_payer_rejected_unack
+    ON claims(payer_rejected_at)
+    WHERE payer_rejected_acknowledged_at IS NULL;